Currently there are a few common ways to print inkjet ink on to non-absorbent media, for example, solvent ink, 100% UV curable ink, and water based dispersion ink (e.g. latex). Solvent inks are relatively inexpensive but they have the drawback that the solvent needs to be evaporated, which poses an environmental risk both to the broader environment and to the workers engaged in printing. In addition, there is a fine balance so that the solvent is sufficiently fast evaporating to enable fast printing at low temperatures, while at the same time being slow enough so that print quality is not degraded by drying of the binder in the print-head or at the nozzles.
100% solid UV curable inks rely on chemistries that cure under actinic radiation. This effectively insures the curing of the ink on the substrate, for example by UV irradiation, while insuring that the ink does not cure in the print-head or at the nozzles. The 100% solid UV curable inks suffer from a few drawbacks. The material in the ink serves as a carrier for the pigment and hence the graphic information. Because these are materials synthesized to cure under light they are relatively costly compared to a simple solvent in a solvent based ink or compared to water in a water based ink.
In order to attain the low viscosities required for piezo print-heads, with some heads requiring a viscosity of 6-7 cP at jetting temperature, some formulated inks rely on small radiation curable monomers that polymerize to give a film. In order to achieve good chemical and physical resistance, these inks need to be highly cross-linked. High cross-linking leads to brittleness. Conversely the inks can be formulated to have a low degree of crosslinking and hence less brittle. In this case, the inks will be less chemically and physically resistant. To enable a low viscosity inkjet ink to cure at a sufficient rate required by today's printers, high levels of monomers and photoinitiators are required, which have the risk to migrate to surrounding environment and thus cause health and safety issues. The risk becomes particularly apparent for all printing that relates to the food, cosmetic or pharmaceutical industry.
Water based latex inks used today often use dispersions having high molecular weight polymers in water that enable a low viscosity fluid. The curing of these latex inks is thermal in nature, so that the mechanism that cures and forms a solid mechanically and chemically resistant film may also cause inadvertent cure of the inks in the nozzles of the print-head, leading to blocked or misdirected nozzles. In order to protect the print-head from inadvertent curing, it is advantageous to design the ink to cure at temperatures well above ambient temperature. These higher cure temperatures restrict the range of media that can be used with these inks.